Metallized fuel emulsion

ABSTRACT

A STABLE SEMI-SOLID OR PSEUDOPLASTIC FUEL CONTAINING UNUSUALLY HIGH AMOUNTS, E.G., 70 WT. PERCENT, OF A METAL SUCH AS BORON, ALUMINUM, ETC., IS PREPARED BY INCORPORATING THE METAL IN A NON-AQUEOUS OR ESSENTIALY NON-AQUEOUS EMULSION CONTAINING AS THE DISPERSED PHASE A MAJOR PROTION OF A HYDROCARBON, E.G., JET FUEL, AN EMULSIFIER AND AS THE CONTINUOUS PHASE A MINOR PROPORTION OF A POLAR ORGANIC LIQUID SUCH AS FORMAMIDE. SUCH EMULSIONS ARE READILY PUMPABLE AND ARE USEFUL AS FUELS IN AIR-BREATHING ROCKETS.

United States Patent Ofiice 3,709,747 METALLIIZED FUEL EMULSION James Nixon, Westfield, Thomas .l. Wallace, Whippany, and Alan Beerhower, Westfield, N..l., assignors to Esso Research and Engineering Company, Linden, NJ. No Drawing. Filed June 16, 1969, Ser. No. 833,660 lint. Cl. C06d /10 US. Cl. 14922 13 Claims ABSTRACT OF THE DISCLOSURE A stable semi-solid or pseudoplastic fuel containing unusually high amounts, e.g., 70 wt. percent, of a metal such as boron, aluminum, etc., is prepared by incorporating the metal in a non-aqueous or essentially non-aqueous emulsion containing as the dispersed phase a major proportion of a hydrocarbon, e.g., jet fuel, an emulsifier and as the continuous phase a minor proportion of a polar organic liquid such as formamide. Such emulsions are readily pumpable and are useful as fuels in air-breathing rockets.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to stable, semi-solid or pseudoplastic emulsions containing a high level of finely-divided metal. In another aspect, the invention relates to emulsified metal-containing fuels which are prepared by coating finely-divided metal with an emulsifier prior to incorporation of the metal into an emulsion having as the dispersed phase a major proportion of a liquid hydrocarbon and having as the continuous phase a minor proportion of a polar organic liquid.

Description of the prior art In volume-limited, air-breathing rockets it is desirable to use a fuel which has a high density. With such a fuel for a given volume it is then possible to significantly increase the range and/ or payload of the rocket. The approach used in the past has been to incorporate metals such as boron or aluminum into a fuel. This has been accomplished by incorporating the metal into a gelled or aqueous fuel emulsion. However, such metal-containing fuels have not been satisfactory since the metal contained in these fuels tends to settle out during storage and transfer.

It has now been found that settling of the metal can be virtually eliminated or significantly reduced by incorporating the metal in the fuel emulsion of this invention. Moreover, as compared to the prior art metal-containing gelled fuels, the present fuel emulsions are readily pumpable. Also, in those embodiments of the invention in which there is no water present, any corrosion problem that has been previously encountered with aqueous emulsions is eliminated. In fact, even in those embodiments in which the total water content does not exceed 0.5 to 1.0 wt. percent any corrosion problem is either essentially nonexistent or at the very minimum very largely eliminated.

SUMMARY OF THE INVENTION In accordance with the present invention, it has now been found that high density fuels having a high degree of stability can be prepared by forming an emulsion containing finely-divided metal, a liquid hydrocarbon as the dispersed phase and a polar organic liquid as the continuous phase together with a small amount of at least one organic emulsifier. Typically, the emulsion will have a yield stress greater than about 1500 dynes per square centimeter (as measured by the ASTM D-2l7 Penetrometer, or by equivalent means or methods such as the 3,709,747 Patented Jan. 9, 1973 ASTM D1092 Viscometer extrapolated back to zero rate of shear, or the rising sphere yield stress method MIL-P- 27421) and may be readily pumped by ordinary vane or gear pumps. In a preferred embodiment, the metalcontaining emulsion of the invention will have a yield stress within the range between about 2500 and 10,000 dynes per square centimeter. As described more fully hereinafter, the emulsion is preferably prepared by coating finely-divided metal with an emulsifier prior to admixture of the metal with the liquid hydrocarbon and polar organic liquid.

The polar organic liquids that are employed as the continuous phase can be characterized as those having dielectric constants greater than 25 and solubility parameters greater than 10. Representative materials include formamide, dimethyl acetamide, diethyl formamide, dimethyl sulfoxide, propylene carbonate, glycidol, ethylene glycol, dimethyl formamide, and combinations thereof. Although it is not a critical feature of the invention, there is some advantage in having the freezing point of the continuous phase be not much above 40 F. so that the emulsion will be stable at relatively low temperatures.

Tabulated below are the characteristics of some of the polar materials that are suitable for use as the continuous or dispersing phase of the emulsions of this invention. For comparison, the properties of Water and of petroleum hydrocarbon jet fuel are also given in the tabulation.

Dielec- Boiling trio conpt., F. stant 1 Calculated as square root of energy of vaporization per unit volume, goal/cc. by method of J. H. Hildebrand "SolubilityoiNon-Eleetrolytes. 3rd Edition, Reinhold Publishing Corporation, New York, 1950. 1 gerlystallizes slowly at this temperature; melting point of crystals is nar.

It is, of course, necessary that the continuous phase liquid be essentially immiscible with the liquid hydrocarbon.

Forrnamide is one substance that is preferred as the continuous phase material for use in this invention because it permits the preparation of an essentially waterfree emulsion. In the case of formamide, low temperature stability can be improved by employing mixtures of formarnide With certain solid amides, provided the mixtures are still liquid at ambient temperatures. The solid amides are characterized as those having from one to three carbons atoms, two amino groups and zero to two imino groups. Such solid amides include urea, oxamide, and guanidine. Usually, in these mixtures from 50 to of the mixture will be formamide and the balance of the mixture will be one or more of the solid amides.

In the case of ethylene glycol, propylene glycol and glycerol, it is possible to eliminate the need for Water in making a stable emulsion by employing a mixture of the glycol or glycerol with from 5 to 30% of urea, or preferably with from 10 to 20% of urea. Also, water-free emulsions can be prepared using a mixture of from 60 to formamide and from 10 to 40% of ethylene glycol. Other completely non-aqueous emulsions in which a glycol or glycerol is employed as the continuous phase are possible by substituting for the water small proportions of a C to C fatty alcohol or fatty acid, e.g. lauryl alcohol.

The hydrocarbons that form the dispersed phase in the emulsions of the present invention include those boiling Solubility parameter 1 within the range of about 70 to 750 F., e.g. petroleum fractions, such as gas oils, kerosene, motor gasoline, aviation gasoline, aviation turbo-jet fuels, diesel fuels, Stoddard solvent, and the like, as well as coal tar hydrocarbons such as coal tar solvent naphtha, benzene, xylene, hydrocarbon fuels from coal gasification, shale oil distillates, and the like. Gasoline is defined as a mixture of liquid hydrocarbons having an initial boiling point in the range of about 70 to 135 F. and a final boiling point in the range of about 250 to 45 F. Most usually gasolines are identified as either motor gasolines or aviation gasolines. Motor gasolines normally having boiling ranges between about 70 and 450 F., while aviation gasolines have narrower boiling ranges between about 100 and 330 F. Gasolines are composed of a mixture of various types of hydrocarbons, including aromatics, olefins, paraffins, isoparafiins, and naphthenes. Stoddard solvent generally has a boiling range of about 300 to 400 F. Diesel fuels include those defined by ASTM Specification D- 975-53T. Jet fuels generally have boiling ranges within the limits of about 150 to 600 F. Jet fuels are usually designated by the terms JP-4, JP-5, or JP-6. JP-4 and JP-S fuels are defined by US. Military Specification MIL- T-5624-G. Aviation turbine fuels boiling in the range of 200 to 550 F. are defined by ASTM Specification D-1655-59I. The following are the characteristics of a typical jet fuel:

JP-4 fuel Reid vapor pressure: 2.20; API gravity: 53.5; freezing point: max. -76 F.

ASTM D-86 distillation F.)

IBP 140 251 20% 278 30% 300 50% 326 80% 383 95% 445 EP 473 A non-metal-containing emulsifier is preferred in the practice of this invention. Although a single emulsifier may be used, the best balance of forces of attraction between the hydrocarbon phase and the continuous phase of the emulsion is obtained by using a combination of two or more emulsifiers. For most satisfactory results, the lipophilic portion of the emulsifier must closely match the particular hydrocarbon or hydrocarbon fraction being dispersed. To attain the proper balance between lipophilic and non-lipophilic (i.e. hydrophilic) forces in the emulsifier system, it is convenient to use the scale of HLB values known to the emulsifier art. These are discussed by W. C. Griffin in the Journal of the Society of Cosmetic Chemistry, December 1948; page 419; also in Kirk-Othmer Encyclopedia of Chemical Technology, second edition, volume 8, pages 131-133 (1965). Desired HLB values can be obtained by using two or more emulsifiers in combination. Briefly, HLB number is ascertained by dividing the molecular weight of the hydrophilic compounds employed in the synthesis of a given compound by the molecular weight of that compound and multiplying the result by 20. In situations where a plurality of materials are employed in the dispersant system, the HLB number for the total system is the summation of the HLB numbers of the individual components multiplied by the weight percent of that particular component of the total dispersant system.

Emulsifiers and emulsifier combinations which give HLB values in the range of 11-16 are satisfactory for producing a stable emulsion in the present invention. Formamide gives an even greater latitude in the selection of emulsifiers that may be used. This is believed to be because of the strong hydrogen bonding and/or polar forces in formamide. Mixtures of formamide and solid amides such as urea appear to give the most satisfactory emulsions when using non-ionic emulsifiers having HLB values in the 11-14 range. With polar organic liquids within the scope of this invention that are used in conjunction with amides or with small amounts of water, such as ethylene glycol, the effective HLB value will depend on the particular liquid selected and will vary with the proportion of water or amide to the said organic liquid constituting the continuous phase.

Among the surfactants or emulsifiers that may be employed in the present invention are included alkyl phenyl poyethylene glycol ethers such as Tergitol NPX of Carbide and Carbon Company; polyethylene polyoxypropylene glycol such as Pluronic L-64 of Wyandotte Chemical Company; rosin acid esters of polyoxyethylene glycol such as Ethofat 242/25 of Armour Industrial Chemical Company; and alkyl phenyl polyethoxy alkanols, such as Triton X-102 which is iso-octyl phenyl polyethoxy ethanol, i.e., the reaction product of iso-octylphenol and ethylene oxide. The alkyl phenyl polyalkoxy alkanols are obtained by reacting 5 to 15 molar proportions of a C to C alkylene oxide with one molar proportion of an alkyl phenol having a C to C alkyl group, e.g., the reaction product of 6 moles of propylene oxide with one mole of dodecyl phenol, the reaction product of a mixture of 5 moles of ethylene oxide and 5 moles of propylene oxide with one mole of nonyl phenol, and the reaction product of 8 to 10 moles of ethylene oxide with one mole of iso-octyl phenol. These are included within a broader class of materials having the formulae:

RA CH CH O CH CI-I OH RA(CH CH OH O CH CH CH OH Where R is a C to C hydrocarbon group, A is oxygen or sulfur and x is 5 to 20.

Other emulsifiers include the fatty acid esters of sorbitan, such as sorbitan monolaurate, sorbitan monostearate, sorbitan monopalmitate and the alkoxylated fatty acid esters of sorbitan such as polyoxyethylene sorbitan mono stearate, tristearate or trioleate. The various sorbitan esters of fatty acids are well known to the art as Spans, and the polyoxyethylene derivatives of the sorbitan esters of fatty acids are well known as Tweens. Still other suitable emulsifiers include N-alkyl trimethylene diamine dioleate of Armour and Company, octakis (2-hydroxy propyl) sucrose, the condensation products of fatty acid amides and ethylene oxide, the ethoxylated fatty alcohols, polyoxyethylene monostearate, polyoxyethylene monolaurate, propylene glycol mono-oleate, glycerol monostearate, ethanolamine fatty acid salts, stearyl dimethyl benzene ammonium chloride, various gums such as gum tragacanth, gum acacia, etc. Where the presence of metal is not objectionable in the emulsion, metal-containing emulsifiers can also be used, such as sodium dioctyl sulfosuccinate (Aerosol OT) or disodium N-octadecyl sulfosuccinamate (Aerosol 18).

An extensive list of emulsifiers together with their HLB values is given in Kirk-Othmer Encyclopedia of Chemical Technology, second edition, vol. 8, pages 128-130 (1965 From this list it is possible to select those that either alone or in admixture will give an HLB value suitable for use in the present invention.

The metal contained in the emulsion of this invention is selected from Groups I-A, II-A, III-A, VII-B, VIII, I-B and I-B of the Periodic Table such as boron, aluminum, barium, manganese, magnesium, beryllium, iron, cobalt, nickel, mixtures thereof and the like. The preferred metals are boron, aluminum, barium, magnesium, and beryllium. The Periodic Table referred to herein is that published in Encyclopedia of Chemistry, Reinhold Publishing Corporation, second edition (1966) at page 790.

The aforedescribed metals which are employed in the emulsion of this invention generally have a particle size Concentration, wt. percent Component Broad Preferred Finely-divided metal (cg. 0.1 to 73. 50 to 70. Hydrocarbon (dispersed phase) 24 to 98 (e.g. 97.9). 27 to 42.5. Polar tgrganic liquid (continuous 1.5 to 15 2 to 5.

p ase Emulsifier 0.5 to 5 1 to 2.5.

In the case where water is employed in the continuous phase, the component ranges will be slightly different, i.e.,

Concentration, Wt. percent In one embodiment of the invention, it has been unexpectedly found that unusually large portions, e.g., 73 wt. percent, of finely-divided metal can be stably suspended in the emulsion when the metal particles are precoated with at least one of the aforedescribed emulsifiers. However, if the metal is not pretreated, i.e., precoated with an emulsifier, only about 45 wt. percent of elemental metal can be readily suspended to form a stable meta-containing emulsion.

The metal particles may be precoated with the emulsifier in several ways and the particular method employed is unimportant provided that a film of emulsifier is deposited on at least a portion of the surface area of the metal particles. The amount of emulsifier deposited on the metal surface is a matter of choice and the amount of metal which can be incorporated into the emulsion of the invention is a function of the proportion of the metal surface precoated with the emulsifier, i.e., as the surface area which is covered with emulsifier is increased the amount of metal which can be used to form a stable emulsion is also increased. A convenient method of coating the metal particles is as follows: metal particles (e.g., 0.10-0.50, preferably 0.10-0.25 micron, average diameter) are contacted with at least one of the aforedescribed emulsifiers dissolved in some solvent (e.g., JP-4 fuel, kerosene, acetone, toluene, etc.) at ambient or moderate temperatures (e.g., 50-100 F.) to form a slurry which is stirred for a period of time (usually to minutes) to eifect the desired proportion of metal surface area to be coated. Typically, the amount of emulsifier used in precoating the metal particles will range from about 0.72 pound of emulsifier per 100 pounds of metal to about 3 pounds of emulsifier per 100 pounds of metal. Particularly good results are achieved when the amount of emulsifier used to precoat the metal is in the range of 0.751.0 pound of emulsifier per 100 pounds of elemental carbon. The mixture is then filtered and the coated metal particles are heated to remove the remaining solvent. The resultant emulsifier-coated metal is then preferably pulverized and sieved through a screen to produce a sufficiently small particle size such as those passing a 30 mesh, preferably 100 mesh, screen (U.S. sieve number).

Another metal pretreatment procedure involves the formation of a metal slurry in the hydrocarbon containing at least one of the aforedescribed emulsifiers. The slurry is then admixed with sufficient polar organic liquid to form an emulsion containing the meal (e.g., wt. percent metal). The resultant emulsion is then vigorously stirred until it is broken and the metal which settles out is recovered by filtration and stripping of the solvent.

The emulsifier-coated metal is then sieved as above in order to produce the desired particle size.

To form the final emulsion, the pretreated or precoated finely-divided metal is preferably added to the hydrocarbon along with at least one of the aforede'scribed emulsifiers (which may or may not be the same emulsifier used to coat the metal) to form a slurry which is then added to the polar organic liquid with stirring to produce the emulsion of the invention.

The nature of the invention will be more fully understood when reference is made to the following examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A number of emulsions having the compositions shown in the following table were prepared and tested. Emulsions A and B were prepared by adding the emulsifiers to a slurry containing the fuel and finely-divided metal (0.25 micron average particle size with particles ranging from 0.1 to 0.5 micron) and then adding the resultant mixture at room temperature over a period of about 2 hours to formamide contained in a vessel agitated with a paddletype low-speed stirrer. Emulsions (C and D were prepared by pretreating the boron employed in Emulsion A before incorporation into the final emulsion. In this pretreatment, 225 grams of boron were added to a mixture containing 225 grams of JP-4 fuel, 0.4 gram of sorbitan monooleate (available as Span from Atlas Chemical Industries, Inc.) and 1.1 grams of polyoxyethylene sorbitan monooleate (available as Tween 80 from Atlas Chemical Industries, Inc.) with stirring at room temperature for about 10 minutes. The mixture was then filtered to isolate the resulting emulsifier-coated boron which was then heated at about 250 F. and atmospheric pressure to remove the JP-4 fuel. The emulsifier-coated boron was then screened to pass a 30 mesh screen (U.S. sieve number) and the material passing through the screen was added to about 5 wt. percent (based on boron) of JP-4 fuel with mixing to form a thick paste which was pulverized using a mortar and pestle. The emulsion was then formed by adding at room temperature a mixture of the paste, JP-4 fuel and emulsifiers over a period of about 1 hour to formamide contained in a vessel agitated with a paddle-type low-speed stirrer.

Wt. percent of component in emulsions Component:

Boron 47. 0 67.0 57. 0 Aluminum 35 JP-4 fuel (dispersed phase). sorbitan monooleate 0. 56 1. 12 0.14 0. 42 Polyoxyethylene sorbitan monooleate 1.44 2. 88 0.36 1. 08

Formamide (polar continuous phase)". 4. 0 4. 0 2.5 2.0 Properties of emulsified fuel:

Yield stress at 77 F., dynes/cm. 1, 750 5, 000 3, 250 5, 400 Stability (8 hours vibration wt. percent separation 0.0 0. 0 0.0 0.0

a As measured by ASTM D-217 test method.

d 350 grams of emulsions placed in glass cylindrical container approximately 8% inches in diameter and 6 inches in height and vibrated at room temperature for 8 hours at 360 cycles per minute developing a force of about 2 g.s at the end of each stroke.

example, the invention emulsions containing metals (or oxides thereof) such as barium, manganese, and the like may be added to fuels, e.g., diesel fuels, gasoline, kerosene, etc., in amounts ranging from about 01% to 0.50% by weight (based on fuel) to improve the combustion and reduce the smoke produced thereby.

It is not intended that this invention be limited to these specific examples presented by way of illustration. The scope of the invention is limited only by the appended claims.

What is claimed is:

1. A stable metal-containing pseudoplastic emulsion, which comprises as a dispersed phase from about 24 wt. percent to less than 98 wt. percent of a liquid hydrocarbon boiling within the range of 70 to 750 F.; from about 1.5 to 15 wt. percent of a polar organic liquid as the continuous phase; from about 0.5 to about wt. percent of an organic emulsifier capable of forming said emulsion; and up to 73 wt. percent of finely-divided metal, said polar organic liquid being selected from the group consisting of formamide; a mixture of formamide with a solid amide having from 1 t0 3 carbon atoms, 2 amino groups and 0 to 2 imino groups; a mixture of formamide with ethylene glycol; and a mixture of urea with ethylene glycol, propylene glycol, or glycerol.

2. The emulsion as defined by claim 1 wherein said emulsifier has an HLB value in the range of about 11 to 16.

3. The emulsion as defined by claim 1 wherein said metal is boron, aluminum, barium, manganese, magnesium, beryllium, iron, cobalt, or nickel or mixtures thereof.

4. The emulsion as defined by claim 1 wherein said metal is boron, aluminum, beryllium, barium, magnesium, or mixtures thereof.

5. The emulsion as defined by claim 1 wherein the amount of said finely-divided metal ranges from 50 to 707 by Weight, the amount of said hydrocarbon ranges prises from about 24 wt. percent to less than 98 wt. percent of the liquid hydrocarbon, from about 1.5 to 15 wt. percent of the polar organic liquid, from 0 to about 1.5 wt. percent water, from about 0.5 to 5 wt. percent of the emulsifier and up to 73 wt. percent of finely-divided metal.

8. The emulsion as defined by claim 1 which comprises from about 27 to 42.5 wt. percent of the liquid hydrocarbon, from about 1.5 to 5 wt. percent of formarnide or a formamide-urea mixture, from about 0.5 to about 1 wt. percent of water, from about 1 to 2.5 wt. percent of the organic emulsifier and to 70 wt. percent of finely-divided metal.

9. The emulsion defined by claim 1 wherein said metal is boron.

10. The emulsion defined by claim 1 wherein said metal is aluminum.

11. A process for preparing a stable pseudoplastic emulsion having a high metal content which comprises:

(a) contacting metal particles with an emulsifier having an HLB value greater than 10 to form metal particles having a coating of said emulsifier; and thereafter (b) admixing said emulsifier-coated metal particles with a liquid hydrocarbon, a polar organic liquid and an emulsifier to form the emulsion defined by claim 1.

12. A process as defined by claim 11 wherein said metal is boron.

13. A process as defined by claim 11 wherein said metal is aluminum.

References Cited UNITED STATES PATENTS 2,927,849 3/ 1960 Greblick et a1 149-22 3,352,109 11/1967 Lissant -217 3,346,494 10/1967 Robbins et al 44--51 X BENJAMIN R. PADGETT, Primary Examiner U.S. Cl. X.R. 445l; 1496, 87 

